Method and system for HSDPA maximum ratio combination (MRC) and equalization switching

ABSTRACT

Aspects of a method and system for a single antenna receiver system for HSDPA are provided. Aspects of a system for processing RF signals, the method may comprise a cluster path processor that computes channel estimates based on at least one of a plurality of received individual distinct path signals. An equalizer may equalize at least one of the plurality of distinct path signals. A maximum ratio combiner may combine at least one of the plurality of distinct path signals. A signal to noise averaging processor may compute at least one estimated signal to noise ratio. An HSDPA switch may select either the equalized plurality of individual distinct path signals, or the combined plurality of individual distinct path signals based on at least one computed signal to noise ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference, claims priority to, and claims thebenefit of U.S. Provisional Application Ser. No. 60/616,905 filed Oct.6, 2004.

This application is related to the following applications, each of whichis incorporated herein by reference in its entirety for all purposes:

-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16199US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16200US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16201US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16203US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16204US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16205US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16206US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16207US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16208US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16209US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16210US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16211US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16212US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16213US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16214US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16215US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16216US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16217US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16218US02) filed ______, 2005;-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16219US02) filed ______, 2005; and-   U.S. patent application Ser. No. ______ (Attorney Docket No.    16220US02) filed ______, 2005.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communication receivers.More specifically, certain embodiments of the invention relate to amethod and system for HSDPA maximum ratio combination (MRC) andequalization switching.

BACKGROUND OF THE INVENTION

Mobile communications has changed the way people communicate and mobilephones have been transformed from a luxury item to an essential part ofevery day life. The use of mobile phones is today dictated by socialsituations, rather than hampered by location or technology. While voiceconnections fulfill the basic need to communicate, and mobile voiceconnections continue to filter even further into the fabric of every daylife, the mobile Internet is the next step in the mobile communicationrevolution. The mobile Internet is poised to become a common source ofeveryday information, and easy, versatile mobile access to this datawill be taken for granted.

Third generation (3G) cellular networks have been specifically designedto fulfill these future demands of the mobile Internet. As theseservices grow in popularity and usage, factors such as cost efficientoptimization of network capacity and quality of service (QoS) willbecome even more essential to cellular operators than it is today. Thesefactors may be achieved with careful network planning and operation,improvements in transmission methods, and advances in receivertechniques. To this end, carriers need technologies that will allow themto increase downlink throughput and, in turn, offer advanced QoScapabilities and speeds that rival those delivered by cable modem and/orDSL service providers. In this regard, networks based on wideband CDMA(WCDMA) technology may make the delivery of data to end users a morefeasible option for today's wireless carriers.

FIG. 1 a is a technology timeline indicating evolution of existing WCDMAspecification to provide increased downlink throughput. Referring toFIG. 1 a, there is shown data rate spaces occupied by various wirelesstechnologies, including General Packet Radio Service (GPRS) 100,Enhanced Data rates for GSM (Global System for Mobile communications)Evolution (EDGE) 102, Universal Mobile Telecommunications System (UMTS)104, and High Speed Downlink Packet Access (HSDPA) 106.

The GPRS and EDGE technologies may be utilized for enhancing the datathroughput of present second generation (2G) systems such as GSM. TheGSM technology may support data rates of up to 14.4 kilobits per second(Kbps), while the GPRS technology, introduced in 2001, may support datarates of up to 115 Kbps by allowing up to 8 data time slots per timedivision multiple access (TDMA) frame. The GSM technology, by contrast,may allow one data time slot per TDMA frame. The EDGE technology,introduced in 2003, may support data rates of up to 384 Kbps. The EDGEtechnology may utilizes 8 phase shift keying (8-PSK) modulation forproviding higher data rates than those that may be achieved by GPRStechnology. The GPRS and EDGE technologies may be referred to as “2.5G”technologies.

The UMTS technology, introduced in 2003, with theoretical data rates ashigh as 2 Mbps, is an adaptation of the WCDMA 3G system by GSM. Onereason for the high data rates that may be achieved by UMTS technologystems from the 5MHz WCDMA channel bandwidths versus the 200 KHz GSMchannel bandwidths. The HSDPA technology is an Internet protocol (IP)based-service, oriented for data communications, which adapts WCDMA tosupport data transfer rates on the order of 10 megabits per second(Mbits/s). Developed by the 3G Partnership Project (3GPP) group, theHSDPA technology achieves higher data rates through a plurality ofmethods. For example, many transmission decisions may be made at thebase station level, which is much closer to the user equipment asopposed to being made at a mobile switching center or office. These mayinclude decisions about the scheduling of data to be transmitted, whendata is to be retransmitted, and assessments about the quality of thetransmission channel. The HSDPA technology may also utilize variablecoding rates. The HSDPA technology may also support 16-level quadratureamplitude modulation (16-QAM) over a high-speed downlink shared channel(HS-DSCH), which permits a plurality of users to share an air interfacechannel

In some instances, HSDPA may provide a two-fold improvement in networkcapacity as well as data speeds up to five times (over 10 Mbit/s) higherthan those in even the most advanced 3G networks. HSDPA may also shortenthe roundtrip time between network and terminal, while reducingvariances in downlink transmission delay. These performance advances maytranslate directly into improved network performance and highersubscriber satisfaction. Since HSDPA is an extension of the GSM family,it also builds directly on the economies of scale offered by the world'smost popular mobile technology. HSDPA may offer breakthrough advances inWCDMA network packet data capacity, enhanced spectral and radio accessnetworks (RAN) hardware efficiencies, and streamlined networkimplementations. Those improvements may directly translate into lowercost-per-bit, faster and more available services, and a network that ispositioned to compete more effectively in the data-centric markets ofthe future.

The capacity, quality and cost/performance advantages of HSDPA yieldmeasurable benefits for network operators, and, in turn, theirsubscribers. For operators, this backwards-compatible upgrade to currentWCDMA networks is a logical and cost-efficient next step in networkevolution. When deployed, HSDPA may co-exist on the same carrier as thecurrent WCDMA Release 99 services, allowing operators to introducegreater capacity and higher data speeds into existing WCDMA networks.Operators may leverage this solution to support a considerably highernumber of high data rate users on a single radio carrier. HSDPA makestrue mass-market mobile IP multimedia possible and will drive theconsumption of data-heavy services while at the same time reducing thecost-per-bit of service delivery, thus boosting both revenue andbottom-line network profits. For data-hungry mobile subscribers, theperformance advantages of HSDPA may translate into shorter serviceresponse times, less delay and faster perceived connections. Users mayalso download packet-data over HSDPA while conducting a simultaneousspeech call.

HSDPA may provide a number of significant performance improvements whencompared to previous or alternative technologies. For example, HSDPAextends the WCDMA bit rates up to 10 Mbps, achieving higher theoreticalpeak rates with higher-order modulation (16-QAM) and with adaptivecoding and modulation schemes. The maximum QPSK bit rate is 5.3 Mbit/sand 10.7 Mbit/s with 16-QAM. Theoretical bit rates of up to 14.4 Mbit/smay be achieved with no channel coding. The terminal capability classesrange from 900 kbit/s to 1.8 Mbit/s with QPSK modulation, and 3.6 Mbit/sand up with 16-QAM modulation. The highest capability class supports themaximum theoretical bit rate of 14.4 Mbit/s.

However, implementing advanced wireless technologies such as WCDMAand/or HSDPA may still require overcoming some architectural hurdles.For example, the RAKE receiver is the most commonly used receiver inCDMA systems, mainly due to its simplicity and reasonable performanceand WCDMA Release 99 networks are designed so that RAKE receivers may beused. A RAKE receiver contains a bank of spreading sequence correlators,each receiving an individual multipath. A RAKE receiver operates onmultiple discrete paths. The received multipath signals can be combinedin several ways, from which maximal ratio combining (MRC) is preferredin a coherent receiver. However, a RAKE receiver may be suboptimal inmany practical systems, for example, its performance may degrade frommultiple access interference (MAI), that is, interference induced byother users in the network.

In the case of a WCDMA downlink, MAI may result from inter-cell andintracell interference. The signals from neighboring base stationscompose intercell interference, which is characterized by scramblingcodes, channels and angles of arrivals different from the desired basestation signal. Spatial equalization may be utilized to suppressinter-cell interference. In a synchronous downlink application,employing orthogonal spreading codes, intra-cell interference may becaused by multipath propagation. Due to the non-zero cross-correlationbetween spreading sequences with arbitrary time shifts, there isinterference between propagation paths (or RAKE fingers) afterdespreading, causing MAI. The level of intra-cell interference dependsstrongly on the channel response. In nearly flat fading channels, thephysical channels remain almost completely orthogonal and intra-cellinterference does not have any significant impact on the receiverperformance. On the other hand, the performance of the RAKE receiver maybe severely deteriorated by intra-cell interference in frequencyselective channels. Frequency selectivity is common for the channels inWCDMA networks.

Due to the difficulties faced when non-linear channel equalizers areapplied to the WCDMA downlink, detection of the desired physical channelwith a non-linear equalizer may result in implementing an interferencecanceller or optimal multi-user receiver. Both types of receivers may beprohibitively complex for mobile terminals and may require informationnot readily available at the mobile terminal. Alternatively, the totalbase station signal may be considered as the desired signal. However,non-linear equalizers rely on prior knowledge of the constellation ofthe desired signal, and this information is not readily available at theWCDMA terminal. The constellation of the total base station signal, thatis, sum of all physical channels, is a high order quadrature amplitudemodulation (QAM) constellation with uneven spacing. The spacing of theconstellation changes constantly due to transmission power control (TPC)and possible power offsets between the control data fields,time-multiplexed to the dedicated physical channels. The constellationorder may also frequently change due to discontinuous transmission. Thismakes an accurate estimation of the constellation practicallyimpossible.

In this regard, the use of multiple transmit and/or receive antennas mayresult in an improved overall system performance. These multi-antennaconfigurations, also known as smart antenna techniques, may be utilizedto mitigate the negative effects of multipath and/or signal interferenceon signal reception. It is anticipated that smart antenna techniques maybe increasingly utilized both in connection with the deployment of basestation infrastructure and mobile subscriber units in cellular systemsto address the increasing capacity demands being placed on thosesystems. These demands arise, in part, from a shift underway fromcurrent voice-based services to next-generation wireless multimediaservices that provide voice, video, and data communication.

The utilization of multiple transmit and/or receive antennas is designedto introduce a diversity gain and to suppress interference generatedwithin the signal reception process. Such diversity gains improve systemperformance by increasing received signal-to-noise ratio, by providingmore robustness against signal interference, and/or by permittinggreater frequency reuse for higher capacity. In communication systemsthat incorporate multi-antenna receivers, a set of M receive antennasmay be utilized to null the effect of (M-1) interferers, for example.Accordingly, N signals may be simultaneously transmitted in the samebandwidth using N transmit antennas, with the transmitted signal thenbeing separated into N respective signals by way of a set of N antennasdeployed at the receiver. Systems that utilize multiple transmit andreceive antennas may be referred to as multiple-input multiple-output(MIMO) systems. One attractive aspect of multi-antenna systems, inparticular MIMO systems, is the significant increase in system capacitythat may be achieved by utilizing these transmission configurations. Fora fixed overall transmitted power, the capacity offered by a MIMOconfiguration may scale with the increased signal-to-noise ratio (SNR).For example, in the case of fading multipath channels, a MIMOconfiguration may increase system capacity by nearly M additionalbits/cycle for each 3-dB increase in SNR.

However, the widespread deployment of multi-antenna systems in wirelesscommunications, particularly in wireless handset devices, has beenlimited by the increased cost that results from increased size,complexity, and power consumption. Providing a separate RF chain foreach transmit and receive antenna is a direct factor that increases thecost of multi-antenna systems. Each RF chain generally comprises a lownoise amplifier (LNA), a filter, a downconverter, and ananalog-to-digital converter (A/D). In certain existing single-antennawireless receivers, the single required RF chain may account for over30% of the receiver's total cost. It is therefore apparent that as thenumber of transmit and receive antennas increases, the systemcomplexity, power consumption, and overall cost may increase. This posesproblems for mobile system designs and applications.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor single antenna receiver system for HSDPA, substantially as shown inand/or described in connection with at least one of the figures, as setforth more completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 a is a technology timeline indicating the evolution of theexisting WCDMA specification to provide increased downlink throughput,in connection with an embodiment of the invention.

FIG. 1 b illustrates an exemplary HSDPA distributed architecture thatachieves low delay link adaptation, in connection with an embodiment ofthe invention.

FIG. 1 c illustrates an exemplary Layer 1 HARQ control situated in abase station to remove retransmission-related scheduling and storingfrom the radio network controller, in connection with an embodiment ofthe invention.

FIG. 1 d is a chart illustrating exemplary average carried loads forHSDPA-based macrocell and microcell systems, in connection with anembodiment of the invention.

FIG. 2 a is a block diagram of an exemplary system for HSDPA maximumratio combination and equalization switching, in accordance with anembodiment of the invention.

FIG. 2 b is a block diagram illustrating exemplary MRC operation, inaccordance with an embodiment of the invention.

FIG. 3 is an exemplary flow chart of steps in output selection for asingle antenna receiver system for HSDPA, in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor HSDPA maximum ratio combination and equalization switching. Inaccordance with an embodiment of the invention, the HSDPA maximum ratiocombination and equalization switching system may be utilized tooptimize modem performance based on MRC/EQ switching and pilot filterbandwidth setting as a function of channel conditions. The invention mayalso provide optimized modem performance with the use of channelestimation for multiple receive antennas as illustrated in U.S.application Ser. No. ______ (Attorney Docket No. 16203US02) filed______, 2004, and U.S. application Ser. No. ______ (Attorney Docket No.16204US02) filed ______, 2004 and are hereby incorporated by referencein their entirety.

FIG. 1 b illustrates an exemplary HSDPA distributed architecture thatachieves low delay link adaptation, in connection with an embodiment ofthe invention. Referring to FIG. 1 b, there is shown terminals 110 and112 and a base station (BS) 114. HSDPA is built on a distributedarchitecture that achieves low delay link adaptation by placing keyprocessing at the BS 114 and thus closer to the air interface asillustrated. HSDPA leverages methods that are well established withinexisting GSM/EDGE standards, including fast physical layer (L1)retransmission combining and link adaptation techniques, to deliversignificantly improved packet data throughput performance between themobile terminals 110 and 112 and the BS 114.

The HSDPA technology employs several important new technologicaladvances. Some of these may comprise scheduling for the downlink packetdata operation at the BS 114, higher order modulation, adaptivemodulation and coding, hybrid automatic repeat request (HARQ), physicallayer feedback of the instantaneous channel condition, and a newtransport channel type known as high-speed downlink shared channel(HS-DSCH) that allows several users to share the air interface channel.When deployed, HSDPA may co-exist on the same carrier as the currentWCDMA and UMTS services, allowing operators to introduce greatercapacity and higher data speeds into existing WCDMA networks. HSDPAreplaces the basic features of WCDMA, such as variable spreading factorand fast power control, with adaptive modulation and coding, extensivemulticode operation, and fast and spectrally efficient retransmissionstrategies. 31 In current-generation WCDMA networks, power controldynamics are on the order of 20 dB in the downlink and 70 dB in theuplink. WCDMA downlink power control dynamics are limited by potentialinterference between users on parallel code channels and by the natureof WCDMA base station implementations. For WCDMA users close to the basestation, power control cannot reduce power optimally, and reducing powerbeyond the 20 dB may therefore have only a marginal impact on capacity.HSDPA, for example, utilizes advanced link adaptation and adaptivemodulation and coding (AMC) to ensure all users enjoy the highestpossible data rate. AMC therefore adapts the modulation scheme andcoding to the quality of the appropriate radio link.

FIG. 1 c illustrates an exemplary Layer 1 HARQ control situated in abase station to remove retransmission-related scheduling and storingfrom the radio network controller, in connection with an embodiment ofthe invention. Referring to FIG. 1 c, there is shown a hybrid automaticrepeat request (HARQ) operation, which is an operation designed toreduce the delay and increase the efficiency of retransmissions. Layer 1HARQ control is situated in the Node B, or base station (BS), 122 thusremoving retransmission-related scheduling and storing from the radionetwork controller (RNC) 120. This HARQ approach avoids hub delay andmeasurably reduces the resulting retransmission delay.

For example, when a link error occurs, due to signal interference orother causes, a mobile terminal 124 may request the retransmission ofthe data packets. While current-generation WCDMA networks handle thoseretransmission requests through the radio network controller 120, HSDPAretransmission requests are managed at the base station 122.Furthermore, received packets are combined at the physical (PHY) layerand retrieved only if successfully decoded. If decoding has failed, thenew transmission is combined with the old transmission before channeldecoding. The HSDPA approach allows previously transmitted frames (thatfailed to be decoded) to be combined with the retransmission. Thiscombining strategy provides improved decoding efficiencies and diversitygains while minimizing the need for additional repeat requests.

While the spreading factor may be fixed, the coding rate may varybetween ¼ and ¾, and the HSDPA specification supports the use of five,10 or 15 multicodes. More robust coding, fast HARQ, and multi-codeoperation eliminates the need for variable spreading factor and alsoallows for more advanced receiver structures in the mobile such asequalizers as apposed to the traditional RAKE receiver used in most CDMAsystems. This approach may also allow users having good signal qualityor higher coding rates and those at the more distant edge of the cellhaving lower coding rates to each receive an optimum available datarate.

By moving data traffic scheduling to the base station 122, and thuscloser to the air interface, and by using information about channelquality, terminal capabilities, QoS, and power/code availability, HSDPAmay achieve more efficient scheduling of data packet transmissions.Moving these intelligent network operations to the base station 122allows the system to take full advantage of short-term variations, andthus to speed and simplify the critical transmission scheduling process.The HSDPA approach may, for example, manage scheduling to track the fastfading of the users and when conditions are favorable to allocate mostof the cell capacity to a single user for a very short period of time.At the base station 122, HSDPA gathers and utilizes estimates of thechannel quality of each active user. This feedback provides currentinformation on a wide range of channel physical layer conditions,including power control, ACK/NACK ratio, QoS, and HSDPA-specific userfeedback.

While WCDMA Release 99 or WCDMA Release 4 may support a downlink channel(DCH) or a downlink shared channel (DSCH), the HSDPA operation providedby WCDMA Release 5 may be carried on a high-speed downlink sharedchannel (HS-DSCH). This higher-speed approach uses a 2-ms frame length,compared to DSCH frame lengths of 10, 20, 40 or 80 ms. DSCH utilizes avariable spreading factor of 4 to 256 chips while HS-DSCH may utilize afixed spreading factor of 16 with a maximum of 15 codes. HS-DSCH maysupports 16-level quadrature amplitude modulation (16-QAM), linkadaptation, and the combining of retransmissions at the physical layerwith HARQ. HSDPA also leverages a high-speed shared control channel(HS-SCCH) to carry the required modulation and retransmissioninformation. An uplink high-speed dedicated physical control channel(HS-DPCCH) carries ARQ acknowledgements, downlink quality feedback andother necessary control information on the uplink.

FIG. 1 d is a chart illustrating exemplary average carried loads forHSDPA-based macrocell and microcell systems, in connection with anembodiment of the invention. Referring to chart 130 in FIG. 1 d, inpractical deployments, HSDPA more than doubles the achievable peak userbit rates compared to WCDMA Release 99. With bit rates that arecomparable to DSL modem rates, HS-DSCH may deliver user bit rates inlarge macrocell environments exceeding 1 Mbit/s, and rates in smallmicrocells up to 5 Mbit/s. The HSDPA approach supports bothnon-real-time UMTS QoS classes and real-time UMTS QoS classes withguaranteed bit rates.

Cell throughput, defined as the total number of bits per secondtransmitted to users through a single cell, increases 100% with HSDPAwhen compared to the WCDMA Release 99. This is because HSDPA's use ofHARQ combines packet retransmission with the earlier transmission, andthus no transmissions are wasted. Higher order modulation schemes, suchas 16-QAM, enable higher bit rates than QPSK-only modulation in WCDMARelease 99, even when the same orthogonal codes are used in bothsystems. The highest throughput may be obtained with low inter-pathinterference and low inter-cell interference conditions. In microcelldesigns, for example, the HS-DSCH may support up to 5 Mbit/s per sectorper carrier, or 1 bit/s/Hz/cell.

FIG. 2 a is a block diagram of an exemplary single antenna receiversystem for HSDPA maximum ratio combining and equalization switching, inaccordance with an embodiment of the invention. Referring to FIG. 2 a,there is shown a chip matched filter block 202, a cluster path processor(CPP) block 204, a maximum ratio combining (MRC) block 208, anequalization (EQ) block 206, an HSDPA switch 210, a despreader block212, a noise estimation and common pilot channel despreader block 214, asignal to noise (SNR) averaging block 216, and a maximum ratio combiningand equalization selection and decision control block 218. The CPP block204 may further comprise a plurality of CPPs 204 a . . . 204 n. Thedespreader block 212 may further comprise a plurality of despreaders 212a . . . 212 n. The noise estimation and common pilot channel despreaderblock 214 may further comprise a noise estimation for MRC block 214 a, acommon pilot channel despreader for MRC block 214 b, a noise estimationfor EQ block 214 c, and a common pilot channel despreader for EQ block214 d. The SNR averaging block 216 may further comprise an SNR averageblock for MRC 216 a, and an SNR average block for EQ 216 b.

The chip matched filter block 202 may comprise suitable logic,circuitry, and/or code that may be adapted to filter a received digitalsignal and to produce complex in-phase and quadrature phase components(I, Q) of the filtered digital signal. In this regard, in an embodimentof the invention, the chip matched filter block 202 may comprise a pairof digital filters that are adapted to filter the I and Q components towithin, for example, the 3.84 mHz bandwidth of W-CDMA baseband.

The cluster path processor (CPP) block 204 may comprise a plurality ofcluster processors that may be adapted to receive and process an outputof the chip matched filter block 202. A signal cluster may comprise anaggregate of individual distinct path signals received over a specifiedtime interval, where the specified time interval may be of sufficientlength to permit a plurality of individual distinct path signals to bereceived prior to the transmission of a subsequent signal cluster. Thecluster path processors 204 a, . . . , 204 n within the cluster pathprocessor 204 block may be partitioned into pairs of processors, whereineach pair of processors is allocated to a single base station transmitsignal. Each base station may transmit from two antennas. The CPP block204 may track the multipath signal cluster transmitted from each basestation transmit antenna. The CPP 204 may also compute complex estimatesof the time varying impulse response of the RF channel, or “channelestimates”, where the channel estimates may represent estimations of theactual time varying impulse response of the RF channel per base stationtransmit antenna, the estimates are denoted ĥ₁ and ĥ₂. Correspondinglock indicators L₁ and L₂ may also be generated by the CPP 204. The lockindicators may provide an indication of which components in thecorresponding estimates comprise valid component values. In oneembodiment of the invention, cluster path processors 204 a, . . . , 204n may be configured to operate in pairs when a transmitted signal istransmitted by two antennas, where the two antennas may be located inthe same base station, or at different base stations. The configurationsin which a receiving antenna receives signals from two transmittingantenna may be described as “receiving modes” in the W-CDMA standard.These receiving modes may comprise closed loop 1 (CL1), close loop 2(CL2), and space time transmit diversity (STTD). The cluster pathprocessor block 204 may be adapted to assign cluster path processorsfrom the CPP block 204 on a per base station basis.

The maximum-ratio combining block 208 may comprise a plurality ofmaximum-ratio combiners. Similarly with the cluster path processors 204,maximum ratio combiners in the maximum-ratio combining block 208 may beassigned on a per base station basis, with the maximum ratio combinersin the maximum-ratio combining block 208 communicating with cluster pathprocessors 204 a . . . 204 n that may be assigned to the same basestations. Maximum ratio combiners in the maximum-ratio combining block208 may receive timing reference signals, T, and channel estimates andlock indicators, (ĥ₁,L₁) and (ĥ₂,L₂), from the corresponding clusterpath processor blocks 204 a . . . 204 n, which may be utilized by themaximum-ratio combining block 208 to process received signals from thechip matched filter block 202. The maximum ratio combining block 208 mayutilize channel estimate components in accordance with the correspondinglock indicator, utilizing channel estimate components that are valid inaccordance with the corresponding lock indicator. Channel estimatecomponents that are not valid, in accordance with the corresponding lockindicator, may not be utilized. The maximum-ratio combining block 208may be adapted to provide a combining scheme or mechanism forimplementing a rake receiver which may be utilized with adaptive antennaarrays to combat noise, fading, and, co-channel interference.

In accordance with an embodiment of the invention, each of the maximumratio combiners in the maximum-ratio combining block 208 may comprisesuitable logic, circuitry, and/or code that may be adapted to addindividual distinct path signals, received from the assigned RF channel,together in such a manner to achieve the highest attainable signal tonoise ratio (SNR). The highest attainable SNR may be based upon amaximal ratio combiner. A maximal ratio combiner is a diversity combinerin which each of the multipath signals from all received multipaths areadded together, each with unique gain. The gain of each multipath beforesumming can be made proportional to the received signal level for themultipath, and inversely proportional to the multipath noise level. Eachof the maximum-ratio combining blocks may be also adapted to utilizeother techniques for signal combining such as selection combiner,switched diversity combiner, equal gain combiner, or optimal combiner.

In various embodiments of the invention, the assignment of fingers inthe maximum-ratio combining block 208 may be based on the timingreference signal, T, from the cluster path processor block 204. Theproportionality constants utilized in the maximum-ratio combining block208 may be based on the valid channel estimates, ĥ₁ and ĥ₂, from thecluster path processor block 204.

The equalizer, or equalization, block 206 may comprise suitable logiccircuitry and/or code that may be adapted to effectively transform thechannel from a frequency selective channel to a flat fading channel. Inthis regard, the equalization block 206 may be adapted to utilize, forexample, an adaptive algorithm to adaptively calculate weights anditeratively search for an optimal weight solution. The equalizationblock 206 may comprise a plurality of equalizers. Similarly with thecluster path processors 204, equalizers in the equalization block 206may be assigned on a per base station basis, with the equalizers in theequalization block 206 communicating with cluster path processors 204 a. . . 204 n that may be assigned to the same base stations. Theequalization block 206 may receive channel estimates and lockindicators, (ĥ₁,L₁) from the corresponding cluster path processor 204 a. . . 204 n, which may be utilized to calculate weights. Theequalization block 206 may utilize channel estimate components inaccordance with the corresponding lock indicator, utilizing channelestimate components that are valid in accordance with the correspondinglock indicator. Channel estimate components that are not valid, inaccordance with the corresponding lock indicator, may not be utilized.In accordance with an embodiment of the invention, the equalizationblock 206 may be adapted to utilize, for example, a least mean square(LMS) algorithm for the weight calculation. The LMS algorithm mayprovide a good compromise between implementation complexity andperformance gains. Notwithstanding, the invention is not limited in thisregard, and other weight calculation algorithms may be utilized.

The HSDPA switch block 210 may comprise suitable logic, circuitry and/orcode that may be adapted to take decision and/or selection outputsignals from the maximum ratio combining and equalization selection anddecision control block 218 and generate an output signal that may bebased on selection of either a received input signal from the maximumratio combining block 208, or a received input signal from theequalization block 206.

The noise estimation blocks 214 a and 214 c, may comprise processors toutilize a received dedicated pilot signal from the MRC 208 and EQ 206,respectively. The dedicated pilot processing is inherent to W-CDMAoperation, and one skilled in the art can construct a noise estimateusing the dedicated pilot as input. The common pilot channel despreaderblocks 214 b and 214 d may construct a signal estimate by postprocessing the common pilot channel signal received from the MRC 208 andEQ 206, respectively. After post processing the channel appears flat,and allows an estimate of the signal to be derived.

The noise estimation and common pilot channel despreader block 214 maytake inputs from MRC block 208, and/or the equalizer block 206. The SNRestimates when taken from the output of the MRC 208 and equalizer 206are what is referred to as “post-processing” outputs. The output fromthe noise estimation block 214 a, and the common pilot channeldespreader block 214 b may be further processed by the SNR averagingblock for MRC 216 a to generate the post-processing output associatedwith the MRC block 208. The output from the noise estimation block 214c, and the common pilot channel despreader block 214 d may be furtherprocessed by the SNR averaging block for EQ 216 b to generate thepost-processing output associated with the EQ block 206. By processingoutput of the MRC 208 and equalizer 206 to obtain signal and noiseparameters in the channel, a mode select signal may be generated by thedecision control block 218 by thresholding the SNR estimates from theMRC 208 and EQ 206, respectively. The mode select signal may be utilizedby the HSPDA switch 210 to select input from either the EQ 206 or MRC208 to be communicated to the despreader block 212 for subsequentprocessing.

The decision control block 218 may also be used to communicate controlof equalization computation. Based on the SNR estimates generated by thepost processing output, it may be advantageous to disable the equalizercomputation thus saving power. When operating the MRC 208 only, thecomputed SNR of the post processing output associated with the MRC 208may rise, exceeding the threshold required to switch on the equalizer206 and improve the system performance.

The despreader block 212 may comprise suitable logic, circuitry, and/orcode that may be adapted to despread received signals that hadpreviously been spread through the application of orthogonal spreadingcodes in the transmitter. Prior to transmission of an informationsignal, known as a “symbol”, the transmitter may have applied anorthogonal spreading code that produced a signal comprising a pluralityof “chips”. The despreader block 212 may be adapted to generate localcodes, for example Gold codes or orthogonal variable spreading factor(OVSF) codes, that may be applied to received signals through a methodwhich may comprise multiplication and accumulation operations.Processing gain may be realized after completion of integration over apre-determined number of chips over which the symbol is modulated.

FIG. 2 b is a block diagram illustrating exemplary MRC operation, inaccordance with an embodiment of the invention. Referring to FIG. 2 b,the maximum-ratio combining (MRC) block 250 may comprise a plurality ofadders 252, . . . , 256, a plurality of multipliers 258, . . . , 264,and a plurality of delay blocks 266, . . . , 270. In one embodiment ofthe invention, the MRC block 250 may receive a plurality of channelestimates h_(ik) (i=0,1, . . . , L-1) from a corresponding cluster pathprocessor block. For example, the MRC block 250 may receive estimatevectors ĥ₁ and ĥ₂ of the actual time varying impulse response of achannel, from a cluster path processor. Each of the estimate vectors ĥ₁and ĥ₂ may comprise a cluster grid of channel estimates h_(ik) (i=0,1, .. . , L-1), where L may indicate the width of the cluster grid ofestimates and may be related to the delay spread of the channel.

In operation, the MRC block 250 may be adapted to implement thefollowing equation:${{mrc}_{k} = {\sum\limits_{i = 0}^{L - 1}\quad{h_{L - 1 - i} \cdot {rx}_{k - i}}}},$where mrc_(k) is the output of the MRC block 250, h_(L-1-l) is theplurality of channel estimates corresponding to a channel estimatevector, such as ĥ₁ and ĥ₂, and rx_(k) is a filtered complex inputsignal. The MRC block 250 may be adapted to add individual distinct pathsignals together in such a manner to achieve a high signal to noiseratio (SNR) in an output signal mrc_(k).

The MRC block 250 may receive a filtered complex signal rx_(k) from achip matched filter (CMF), for example. The filtered complex signalrx_(k) may comprise in-phase (I) and quadrature (Q) components of areceived signal. Furthermore, the filtered complex signal rx_(k) may begated by cluster path processor (CPP) output strobes derived from a CPPtiming reference, for example. Channel estimates h_(ik) (i=0,1, . . . ,L-1) may be applied to the CMF output rx_(k) beginning with the last intime, h_(L-1), and proceeding with channel estimates h_(L-2), . . . ,h₀, utilizing multiplier blocks 258, . . . , 264, respectively. Thefiltered complex input signal rx_(k) may be continuously delayed bydelay blocks 266, . . . , 270. Each delayed output of the delay blocks266, . . . , 270 may be multiplied by the multiplier blocks 260, . . . ,264, respectively, utilizing corresponding channel estimates hi_(k). Theoutputs of the multipliers 252, . . . , 256 may be added to generate theoutput signal mrc_(k), thereby implementing the above-referenced MRCequation.

FIG. 3 is a flow chart illustrating exemplary steps for output selectionin a single antenna receiver system HSDPA, in accordance with anembodiment of the invention. With reference to FIG. 3, in step 302channel estimates and a timing reference signal may be generated. Instep 304, signal and noise estimates may be computed based on a signalreceived from the maximum ratio combining block 208 and the equalizationblock 206, respectively. A mode select signal may be generated. In step306, the HSDPA switch 210 may utilize the mode select signal to selectan input signal received from either the EQ 206, or the MRC 208. Anoutput signal may be generated based on the selected input signal. Instep 310, the output signal generated by the HSDPA switch 210 may bedespread by the despreader 212.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for processing radio frequency (RF) signals, the methodcomprising: computing channel estimates based on at least one of aplurality of received individual distinct path signals; equalizing saidat least one of said plurality of individual distinct path signals;combining said at least one of said plurality of individual distinctpath signals; computing at least one estimated signal to noise ratio;and selecting one of: said equalized said at least one of said pluralityof individual distinct path signals, and said combined said at least oneof said plurality of individual distinct path signals, based on saidcomputed at least one estimated signal to noise ratio.
 2. The methodaccording to claim 1, wherein said equalizing is based on said computedchannel estimates.
 3. The method according to claim 1, wherein saidcombining is based on said computed channel estimates.
 4. The methodaccording to claim 1, further comprising computing at least one of: anoise estimate, and a signal level estimate based on said combined saidat least one of said plurality of individual distinct path signals. 5.The method according to claim 1, further comprising computing at leastone of: a noise estimate, and a signal level estimate based on saidequalized said at least one of said plurality of individual distinctpath signals.
 6. The method according to claim 1, further comprisingcomputing said at least one estimated signal to noise ratio based on acomputed noise estimate and a computed signal level estimate based onsaid combined said at least one of said plurality of individual distinctpath signals.
 7. The method according to claim 1, further comprisingcomputing said at least one estimated signal to noise ratio based on acomputed noise estimate and a computed signal level estimate based onsaid equalized said at least one of said plurality of individualdistinct path signals.
 8. The method according to claim 1, furthercomprising generating a mode selection signal based on said at least oneestimated signal to noise ratio.
 9. The method according to claim 1,further comprising selecting said one of: said equalized said at leastone of said plurality of individual distinct path signals, and saidcombined said at least one of said plurality of individual distinct pathsignals, based on said mode selection signal.
 10. The method accordingto claim 1, wherein said equalizing is based on said at least oneestimated signal to noise ratio.
 11. A system for processing radiofrequency (RF) signals, the system comprising: a cluster path processorthat computes channel estimates based on at least one of a plurality ofreceived individual distinct path signals; an equalizer that equalizessaid at least one of said plurality of individual distinct path signals;a maximum ratio combiner that combines said at least one of saidplurality of individual distinct path signals; a signal to noiseaveraging processor that computes at least one estimated signal to noiseratio; and an HSDPA switch that selects one of: said equalized said atleast one of said plurality of individual distinct path signals, andsaid combined said at least one of said plurality of individual distinctpath signals, based on said computed at least one estimated signal tonoise ratio.
 12. The system according to claim 11, wherein saidequalizing is based on said computed channel estimates.
 13. The systemaccording to claim 11, wherein said combining is based on said computedchannel estimates.
 14. The system according to claim 11, furthercomprising a noise estimation and common pilot channel despreader thatcomputes at least one of: a noise estimate, and a signal level estimatebased on said combined said at least one of said plurality of individualdistinct path signals.
 15. The system according to claim 11, furthercomprising a noise estimation and common pilot channel despreader thatcomputes at least one of: a noise estimate, and a signal level estimatebased on said equalized said at least one of said plurality ofindividual distinct path signals.
 16. The system according to claim 11,wherein said signal to noise averaging processor computes said at leastone estimated signal to noise ratio based on a computed noise estimateand a computed signal level estimate based on said combined said atleast one of said plurality of individual distinct path signals.
 17. Thesystem according to claim 11, wherein said signal to noise averagingprocessor computes said at least one estimated signal to noise ratiobased on a computed noise estimate and a computed signal level estimatebased on said equalized said at least one of said plurality ofindividual distinct path signals.
 18. The system according to claim 11,further comprising a maximum ratio combining and equalization selectionand decision control processor that generates a mode selection signalbased on said at least one estimated signal to noise ratio.
 19. Thesystem according to claim 11, wherein said HSDPA switch selects said oneof: said equalized said at least one of said plurality of individualdistinct path signals, and said combined said at least one of saidplurality of individual distinct path signals, based on said modeselection signal.
 20. The system according to claim 11, wherein saidequalizing is based on said at least one estimated signal to noiseratio.